For continuous working, i.e. in particular mixing and kneading, of flowable, i.e. liquid, viscous, plastic or particulate, substances, so-called kneading blocks consisting of disk cams disposed offset in the manner of a spiral staircase are used in twin-shaft extruders (cf. DE-C-813154). The substance is pressed through a narrow tapered gap between the disk cams and the extruder housing, which can result in different heating and partial overstressing by shearing of the substance, and further causes locally above-average wear.
DE-A-2 003 593 already discloses a twin-shaft extruder wherein the screw flight of one screw is sealed by a sealing bar while the other screw has a recess at the place in the screw crest that moves past said sealing bar upon rotation. Here, too, the material blocked with the sealing bar in the flight of the screw is subjected to high stress, while the screw with the recess makes only a small contribution to working the substance.
The problem of the invention is to convert the driving energy of the extruder optimally into uniform working and treatment of the substance.